One embodiment relates to a composite including a ceramic multilayer body, including a cermet feedthrough; to a process for manufacturing a composite, including a cermet feedthrough; to a composite obtainable by the process; to a device including a composite according to one embodiment; and to a use of a composite.
The prior art knows numerous implantable electrical medical devices, for example pacemakers and defibrillators. Pacemakers known in the prior art include a bladder pacemaker, a breath pacemaker, an intestinal pacemaker, a diaphragm pacemaker, a cerebral pacemaker and a cardiac pacemaker. Such devices commonly include a housing enclosing electronics. An electrical source of energy, for example, a battery, may be included by the housing as well or it may be included by a further housing and be connected to the electronics via electrical connectors. The housing which is to be implanted into a human or animal body must hermetically seal the electronics from the surrounding body, that is, it must be leak tight for body fluids and gases. Commonly an object of an implantable electrical medical device involves electrically stimulating tissue, that is, muscles or brain cells, via electrodes or measuring electrical signals of the body via antennae, or both. Therefore, the implantable electrical medical device has to include an electrical feedthrough which electrically connects the inside of the housing to the outside. Such a feedthrough has to be designed to maintain the housing hermetically tight and thus the device implantable. Therefore, an electrical feedthrough for implantable medical devices commonly known in the prior art includes an electrically conductive feedthrough element, here a metal feedthrough wire, which is enclosed by a ceramic ring. Therein, the feedthrough wire is soldered to the ceramic ring via a gold solder. The ceramic ring in turn is soldered into a metal flange, which can be welded to a metal housing. The feedthrough assembly of the prior art includes several intermaterial connections which may be prone to breaking or leaking. In addition, establishing such intermaterial connections is costly or makes a production process more complicated or lengthy. An improved feedthrough is disclosed in EP 1 897 588 B1. Therein, the metal feedthrough wire is connected to a surrounding ceramic body by means of sintering. This way the number of intermaterial connections and the amount of gold solder used are reduced. The connection between the electrically conductive feedthrough element and the ceramic body could be improved by means of the disclosure of DE 10 2009 035 972 A1. Therein, a feedthrough element made of a cermet is used instead of a metal feedthrough element. In order to tailor a ceramic body of a desired thickness or quality or both the ceramic body can include multiple ceramic layers. The feedthrough element then electrically connects through the ceramic layers of the ceramic body. Such a multilayer feedthrough may be prepared by stacking and laminating ceramic green sheet tapes, providing holes which connect through the laminate of the green sheet tapes, filling a cermet into the holes and sintering the green sheet tapes and the cermet together by firing. Such co-fired technology has been implemented with low temperature co-fired ceramic (LTCC) as well as with high temperature co-fired ceramic (HTCC).
In view of the increasing technical demands of modern cermet-based feed through elements it is often required that the top and the bottoms cermet contacts of a feedthrough element are not congruent when being projected onto a horizontal plane. This is, for example, the case if in a given feedthrough element the cermet contacts at the top surface and the cermet contacts on the bottom surface have to be arranged in a different geometry, particularly in a different density. In case of a feedthrough element that is prepared by the above described LTCC- or HTCC-technique this requires that some sort of horizontal connection between the cermet element of the top green sheet (forming a contact on the top surface) and the cermet element of the bottom green sheet (forming a contact on the top surface) has to be realized by the cermet elements of the internal green sheets to somehow bridge the horizontal offset between the top and the bottom cermet element. In EP 3 041 046 A1 this offset is bridged by proving a conductive material onto the top surface of an intermediate green sheet, wherein the surface area of the conductive material is large enough to ensure an electrical connection between the cermet elements of neighboured green sheets shifted relative to each other in the horizontal plane (see, for example, FIGS. 6-8). One disadvantage of this concept, however, has to be seen that an additional process step is required to provide such a conductive material on the surface of a green sheet element. Furthermore, the provision of a conductive material between the interfaces of two green sheets that are located adjacent to each other may lead to the formation of air gaps between these layers in the final composite and to an increase of the risk of delamination. For these and other reasons, a need exists for the present embodiments.